FIG. 1, numeral 100, shows an ATM system in which ATM 5 source (102) and destination (110) end systems are coupled with an ATM network. The ATM network includes: a source edge node (104), a destination edge node (108), and, where selected, one or more intermediate switching nodes (106). ATM cells generated by the source end system are transmitted via the source edge node to intermediate nodes, then to a destination edge node, and lastly to the destination end system. Clearly, ATM networks are subject to congestion when the traffic offered to the network exceeds the capacity of the network. Thus, congestion conditions need to be controlled in order to guarantee, for each ATM connection, the Quality of Service (QOS) negotiated between the communicating end systems and ATM network during call establishment.
Hence, the goals of an effective ATM congestion control scheme should include: (1) guaranteeing that the Quality of Service (QOS) provided to each connection should, at a minimum, satisfy the agreed QOS negotiated during connection establishment; (2) allowing a connection to exceed its agreed throughput QOS if there is unused or unallocated capacity along its path through the network; and (3) in a congested network, informing connections that are exceeding their negotiated traffic parameters of the congested condition and giving an opportunity to reduce rate before the network begins to discard traffic in excess of the negotiated traffic parameters.
Controlling congestion in an ATM network requires effectively regulation of the flow of cells for each connection entering the network at the source end system. Making effective use of unallocated or unused capacity in the network requires feedback signaling to the end systems to properly regulate the flow of cells entering the network. It is important, however, to couple this cell flow regulation to the agreed QOS guarantees for the connection. Even though a number of types of congestion control exist, no existing techniques are available that effectively control the cell flow for a connection from an end system and couple this with QOS guarantees. Thus, there is a need for a device and method for regulating cell flow between ATM source and destination end systems such that congestion is controlled and unused or unallocated capacity is utilized while maintaining QOS guarantees.